'It's an ongoing issue for us,' said Brian Dunbar, a spokesman for NASA headquarters in Washington. 'We're under a fairly constant level of attack here, everything from sophisticated attacks to kids downloading scripts and seeing if we've left any wide open doors for them. People are always trying to compromise our security systems, so it's just going to be a matter of paying closer attention to it for a while.'

Dunbar said he wasn't aware of any increase in network breaches in the aftermath of the attacks.

NASA's systems were up and working normally 'as far as I've been able to see,' Dunbar said. 'There hasn't been a Web site that I've tried to get to yet that wasn't available.'

Nothing up my sleeve

Officials notified employees on NASA's Web site Tuesday night that the agency's 10 centers would be open only for limited operations requiring essential personnel.

Employees who reported for work on Wednesday were carefully searched, Dunbar said.

The increase in security was welcomed by feds who had watched in horror as their colleagues and other innocents came under attack.

'We thought the first incident [at the World Trade Center] was an accident, and the first reaction was disbelief,' Smith said. 'When we realized that it was a terrorist attack, it was total disbelief. We were stunned.'

Most employees watched the events unfold on television, she said, adding 'there was a calm, like after a storm had swept through. When we got the orders to shut down, there was no panic. Our staff handled it very well.'

Smith, who endured two bomb scares when she worked at the Energy Department during the Gulf War, said, 'The good thing about technology in these times is that there is no way not to know what's happening. It was either the computer, television, radio or e-mail.'

Federal workers return to work quickly following tragedy

'It was almost like watching a science fiction movie with all the nasty things happening to New York,' Ditmeyer said.

'There were no tears, no trauma, maybe just disbelief,' he said. 'We stepped out of the building and saw the smoke out of the Pentagon. There were no tears, no anger. It was just strange.'

At the IRS Oversight Board office in Washington, board chief Larry R. Levitan cancelled meetings scheduled for last Wednesday and Thursday. But he indicated that security concerns were not the cause of the cancellations.

'I don't feel under any personal danger,' Levitan said. 'Our country has so much power. Despite having seen it live, I don't think it's going to happen again.'